Grote et al. (2011) integrated dimensional tree growth and mortality routines with MoBiLE-PSIM, a physiologically based process model, to enable quantification of the impacts of direct and indriect impacts of forest management on carbon balances within ecosystems.
Simulations were performed using microclimate, water cycle, soil nutrient dynamics, physiology and dimensional change models combined in a MOBiLE (Grote et al., 2008) framework. The framework manages the exchange of variables between models and modules that describe the cycling of water, carbon and nitrogen in the biosphere, atmosphere and hydrosphere. An Empirical-based Canopy Model (Grote et al., 2009a) is used to provide hourly climatic information for canopy layers and DNDC calculates soil temperature, which drives biogeochemical calculations. The DNDC water balance module is used to calculate water availability and DNDC calculations are used to to simulate the mineralisation, nitrification and denitrification above and below ground. PSIM and DNDC were linked previously in Grote et al. (2009b) by plant uptake of nitrogen. The DNDC model used in the MoBiLE framework is able to calculate '"water pools and fluxes throughout the total rooted soil profile with soil layer specific parameterisations", unlike in the orginal version. A physiology based model, PSIM, simulates further vegetation processes such as plant respiration, senescence and allocation of carbon and nitrogen and nitrogen uptake.
Simulations are site specific and information is only exchanged vertically (from the top of the vegetation to the total rooting depth in the soil) between time steps, as it is 1-D column modelling. The vertical dimension is divided into flexible vegetation layers, of equal height, and a variety of soil layers (defined by C content, N content, field capacity, wilting point, pH, saturated conductivity, clay and stone content, bulk density). The model operates on either a sub-daily, daily or any multiple of day time steps. Vegetation information required includes species, height, canopy length, average diameter at 1.3m, total stem volume, total above ground biomass and tree number.
MoBiLE-DNDC was shown to be capable of simulating carbon fluxes in various types of pureforests, which covered old to young forests and a variety of species (deciduous, evergreen, needle and broad leaved) by Grote et al. (2011). The model is able to quantify real management impacts on the carbon cycle (the model recognises losses from thinning) and there feedback effects, which signifies progress in carbon flux modelling.MoBiLE-DNDC was adapted by Wolf et al. (2012) to examine nitrous oxide emissions during freeze-thaw events in temperate ecoystems, through the addition of routines that relate maximum snow height to end of season biomass (ESSB). The model was developed to better simulate plant production, snow height and soil moisture for steppe terrain exposed to different grazing intensities in Mongolia. The new routines account for decreased plant productivity resulting from grazing and the increase of impedance of soil ice on soil hydraulic conductivity. Modelling impedance within MoBiLE-DNDC improved simulation of soil water content and decreased the oxygen content in the top soil during periods of freeze-thaw. Nitrous oxide emissions were shown to decrease during spring thaw as a result of lower water content and anaerobiosis, which was also observed in field observations.